Printed electronic circuits have certain manufacturing issues that are not necessarily similar to conventional circuit photolithographically defined circuits. First, printing techniques may have relatively poor layer to layer registration, resulting in relatively large overlay allowances. Second, printing techniques generally have lower resolution than photolithography, and some printing techniques may have asymmetric resolution limits (i.e., resolution along one dimension differs from resolution along a different dimension). Third, printing techniques often exhibit proximity and shape-related effects such as wicking, merging of nearby/adjacent patterns, etc., that result in non-ideal pattern generation.
In various printing processes, liquid inks may be selectively deposited (e.g., printed) using a technique such as inkjet printing, gravure printing, screen printing, flexographic printing, etc. Printed electronics offer the potential to reduce the processing cost of conventional semiconductor and/or integrated circuit manufacturing, generally by using additive deposition of electronic inks (e.g., an ink containing one or more precursor[s] for forming a doped or undoped semiconductive, conductive, or dielectric structure or film) to produce electronic features (e.g., electrically functional or insulative structures or films). This approach to forming printed structures may be cost effective due to (i) the efficient usage of the precursor materials and (ii) the combination of deposition and patterning into one printing step. The use of doped or undoped conductive, semiconductive, and dielectric inks to form electrical structures may reduce or minimize the number of masking, photolithography, and etching steps in fabricating integrated circuits and/or structures therein.
Therefore, there is significant motivation within the integrated circuit and display manufacturing industries to develop methods of forming electronic devices using ink technologies. However, printing such electronic inks presents special issues because of the potential of liquids to show dynamic spreading on surfaces. Such spreading may be associated with the wetting and evaporation characteristics of the ink(s). Also, the inks can exhibit proximity and shape-related effects such as merging of nearby or adjacent patterns, which can result in significant and sometimes fatal deviations from the intended pattern.
Generally, the resolution, layer-to-layer registration, and pattern fidelity (in terms of sharpness of corners, line-edge roughness, etc.) of structures formed by printing methods are inferior to that of conventional optical photolithographic techniques. However, printing offers desirable benefits, such as cost efficiency and smooth (e.g., dome-shaped) structure profiles that allow for smooth transitions between layers in a circuit (e.g., without encountering sharp steps and providing more complete and/or uniform step coverage of subsequently deposited structures). Printing techniques sometimes suffer from degraded resolution as well as asymmetric resolution limits (e.g., the resolution in one direction [e.g., the x-axis] may be different from the resolution in another direction [e.g., the y-axis]).
In addition, pattern fidelity may also be an issue with printed circuit features. For example, in conventional optical lithography, laying out shapes as irregular polygons is not particularly problematic. However, such shapes are not particularly suited for printing techniques, due to wetting and wicking effects of the ink.
FIG. 1 shows a conventional layout approach in which each of a first layout 10 for semiconductor islands 11-16 and a second layout 20 for gates 21-29 include irregular shapes (e.g., 12, 14, 16 and 22-27). This is the general approach and/or practice for Application Specific Integrated Circuit (ASIC) designs using traditional photolithographic processes. Printing of electronic inks using these conventional layouts can be difficult, because features generally cannot be printed at the minimum dimensions achievable by photolithography, and inks printed in an irregular geometry and/or on a non-planar or non-uniform surface may be adversely affected by liquid-phase physical phenomena (e.g., deviations from the ideal/target pattern due to spreading, wicking along an underlying topography or surface energy, beading due to surface tension effects, etc.).